Balers are agricultural machines that pick up crop material, such as straw or grass or another crop, lying in a field in swaths and compact the crop material into wrapped or bound bales. The swaths are laid by a combine harvester which, after harvesting the crop, separates the grain from the shafts and the chaff, stores the grain, disperses the chaff and deposits the shafts as swaths on the field being harvested.
There are two varieties of balers, namely round balers and square balers. As their names imply, round balers produce cylindrical bales of round cross section while square balers produce bales of square cross section.
EP 1935233 describes a round baler having a baling chamber fitted with non-contact sensors capable of determining the relative density of the crop in different parts of a bale as it is being formed. A cylindrical bale often has an axial length greater than the width of the swaths on the ground that the baler is picking up. If the operator steers the baler, which may either be self-propelled or towed by a tractor, so that the swath remains central in relation to the baling chamber, then the formed bale will have a higher density at its centre than at its ends. This leads to various problems as described in EP 1935233. To assist the operator in driving the baler to optimise the distribution of the crop across the width of the baling chamber density sensors are provided in the baling chamber.
The same problem of uneven crop density distribution can arise in a square baler but the solution of providing non-contact sensors in the baling chamber does not work for square balers. A first reason for this is that, in a round baler, the crop is constantly circulated past the non-contact sensors and the signal from the sensors varies significantly with the crop density. By contrast, in a square baler, a bale grows slowly and the signal from a sensor placed randomly in the baling chamber would not indicate the crop density in different parts of the bale. A second reason is that the crop density in the baling chamber of a square baler is greater than in a round baler, which makes it more difficult for such a sensor in the baling chamber to be able to determine relative density in different parts of the bale. Such a non-contact sensor measures the proportion of the crop and the voids in between. At such high densities there are approximately no measurable voids in between the crop and the signal of the non-contact sensor remains approximately constant during a change in the density.